You're using a poor metric to define the success of raiding. There were undeniably more people raiding in 10M HC guilds but not because it was better, but because it was easier to organize. You're not bursting my bubble on anything because I personally believe the quality of the raid itself should always usurp the participation levels. WoD, by and large, had much better tuned encounters than anything in MoP/Cata and I'm personally glad they did away with a design philosophy which required them to make two versions of the same thing.
You can disagree with me on this point if you'd like, but the fact that Mythic is sticking around for Legion speaks volumes for what the developers feel as well.